A dental prosthesis—be it crowns, bridges, a partial prosthesis or a total prosthesis—consists of an outer shell and a marginal part, which usually consists of a framework. The outer shell must satisfy aesthetic requirements and, depending on the tooth, allow for functionally suitable articulation. The marginal part must be designed in such a way that the prosthesis can be anchored securely in the mouth of the patient—permanently or removably.
Conventional dental prostheses are individually made by hand. Design and fabrication are carried out from the prepared tooth outward to the outer shell, which is completed only after the marginal part with one or more frameworks has been constructed.
Patients who require a dental prosthesis go through the following phases: Anamnesis is followed by the examination, followed by diagnosis and the selection of a therapy. Afterwards, the actual treatment commences with the hygiene phase and pre-prosthetic preliminary treatment. After completion of said preliminary treatment, the prosthetic work can commence with planning and fabrication of the special crowns or bridges, the partial or total prosthetic care.
For the realization of crown or bridge tooth replacement, it is common today to carry out a test preparation on the gypsum model before the preparation on the patient and after the casting and construction of the model. Depending on the form in which the fabrication of temporary replacements is planned, an alginate or silicone casting, a deep-drawn foil or a temporary shell model must be constructed before the grinding of the tooth, which is to be replaced. Furthermore, it is recommended to select the color prior to the preparation.
During preparation, several issues have to be considered: protection of the pulp, protection of the marginal paradontium as well as obtainment of a retention and resistance form, taking into account materials-technological, construction-related, and aesthetic factors.
Preparation and cleaning of the ground tooth remnant is followed by the definitive casting. A model is subsequently produced in the lab. In case of a combination of fixed and removable tooth replacement, e.g., the following method is applied:
At first, the preparation model and the inner crowns are produced. At the clinic, the fitting of the inner crowns (primary crowns) and the fixation casting are carried out. In the next step, the construction model and jaw relation record are fabricated in the lab. Facial arc transfer, jaw relation determination, and model assembly are, once again, carried out at the clinic. Now, the tooth set-up in wax is prepared at the lab and subsequently fitted at the clinic. In the next step, the outer crowns (secondary crowns) and the connecting framework (tertiary structure) are fabricated. The design and processing of the frameworks mainly adheres to aesthetic aspects; therefore, the framework is produced as delicately as possible, even at the expense of its service life. In practice, a sufficient dimensioning of the frameworks cannot be controlled with complete accuracy.
The build-up of the ceramic masses onto the metal framework—the thermal expansion coefficients of which must be matched—is carried out through mixing of ceramic powder with distilled water and application of the resulting sludge with a brush onto the areas to be encrusted. The ceramic masses are layered in portions next to and/or on top of each other. The resulting form, which varies with the skill of the individual dental technician, is subsequently sintered in the ceramic kiln at the appropriate temperature. The results are not identically reproducible, particularly for structures which include several teeth.
Now, the connecting framework together with the definitive tooth set-up in wax is fitted once again at the clinic.
During the same sitting, a possible aesthetic processing can also be carried out. The functional and aesthetic shell of the tooth replacement emerges during the last step of the process and is not—or only in a very limited fashion—foreseeable during the planning phase. Subsequently, the surfaces are mechanically polished. Finally, the tooth replacement is integrated according to known methods.
The disadvantage of the methods used to this date relates to the construction of the tooth replacement from the inside out, i.e., the outer aesthetic shell is determined only during the last step. Patient, dentist, and dental technician have no or only a vague idea how the finished tooth replacement will look since the result essentially depends on the manual skills of the dental technician.
Particularly, the patient cannot reach any sound joint decision when questions regarding aesthetics versus stability and function are to be assessed. Furthermore, the known method consists of many individual steps to be executed successively, and the patient has to live with a temporary replacement and many fittings for a long time.